1. Field of the Invention
The present invention relates to a document reading apparatus such as a scanner, and in particular to a document reading apparatus provided with a light source assembly for fixing a light source at a predetermined position.
2. Description of the Related Art
There has been utilized a document reading apparatus in which a light beam from a light source (lamp) is applied to a document and the light reflected by the document is detected by a photo sensor such as a CCD (charge-coupled device) image sensor. In the case where the light source for such a document reading apparatus is realized by one having a high luminance such as a mercury lamp, there can be obtained a sufficient quantity of light without taking any measures. However, when adopting one having a lower luminance such as a xenon tube, it is necessary to enhance the quantity of light to be applied to the document. There has been accordingly adopted such a measure that the light beam emitted from a lamp is reflected by a reflector or the like to enhance the quantity of light with which the document is illuminated.
In a conventional document reading apparatus, however, the reflector for reflecting the light emitted from the lamp is provided independently of a lamp fixing member for mount the lamp to a frame in the document reading apparatus. This causes the increased number of parts and the increased cost of the document reading apparatus and further it becomes difficult to simplify the work of assembling and maintenance of the document reading apparatus.
Another conventional light source assembly has been disclosed in Japanese Patent Application Laid-Open No. 1-221975 (229875/1989). This conventional light source assembly is provided with a lamp cover having an opening formed therein. The opening is designed to suppress the undesired illumination of the document.
Since the lamp cover shields the undesired light, however, the effective use of the light emitted from the light source cannot be achieved. In other words, such a conventional light source assembly requires one having a high luminance such as a mercury lamp.
It is therefore an object of the present invention to provide a light source assembly and a document reading apparatus which can achieve the reduced number of parts and the simplified work of assembling and maintenance of the document reading apparatus.
It is another object of the present invention to provide a light source assembly and a document reading apparatus which can achieve the effective use of light emitted from the light source with reliable information reading.
According to an aspect of the present invention, a light-source assembly fixes a light source which is used to illuminate a document, wherein light reflected from the document is received by an image sensor through an-image formation optical system. The light-source assembly includes a plate and a holder. The plate has a reflective surface at one side thereof and a fixing surface at the other side thereof, wherein the plate is fixed at the fixing surface such that the reflective surface is placed in a predetermined direction. The holder is provided on the reflective surface of the one side of the plate. The holder holds and fixes the light source substantially parallel to the reflective surface.
The plate may be formed in a shape changing in width so that a difference in luminance among light receiving positions in the Image sensor is reduced. The plate may be formed in a shape having its width progressively decreasing toward a center portion of the light source
The holder may be composed of a snap-fitting member for holding and fixing the light source, and a supporting member fixed to the plate at one end thereof, for supporting the snap-fitting member at the other end thereof such that the light source is placed substantially parallel to the reflective surface. Preferably, the snap-fitting member has a hollow-cylindrical shape for holding the light source, wherein the snap-fitting member is made of elastic material
Further, the plate may be formed in a rectangular shape. Alternatively, the plate may be formed in a shape having its width progressively decreasing toward a center portion of the light source.
Furthermore, the plate may be provided with a pair of holders provided on the reflective surface of the one side of the plate, wherein the holders hold and fix the light source substantially parallel to the reflective surface.
According to another aspect of the present invention, a document reading apparatus includes a light source for illuminating a document; a light-source assembly for fixing the light source; an Image sensor for sensing an optical image formed thereon; and an optical system for forming the optical image on the image sensor from light reflected from the document. The light-source assembly includes the plate and the holder as described above.